1. Technical Field of the Invention
The present invention relates in general to the cellular communications field and, in particular, to a method and system for reallocating multiple channels in an Automatic Frequency Allocation (AFA) environment.
2. Description of Related Art
In order to obtain reliable statistics while using an automatic process to improve frequency allocations in a cellular communications network based on signal strength measurements (e.g., AFA), an important objective is to conduct the measurements over a relatively long period of time. As such, in order to reduce the time needed to improve such a network""s frequency plan, another important objective is to make more than one frequency reallocation per measurement period. However, a solution to meeting this objective is not a trivial one, because, for example, the measurement results may suggest allocating the same frequency in two relatively near or contiguous cells. If the measurement process being used determines there are two xe2x80x9cbadxe2x80x9d frequencies in two neighboring cells, typically the automated frequency allocation process (e.g., AFA) will suggest that the two frequencies be replaced by one and the same xe2x80x9cgoodxe2x80x9d frequency. However, this approach is problematic, because the two neighboring cells may interfere with each other to a great extent after the reallocation occurs. Consequently, the problem of determining how to make more than one frequency reallocation per measurement period still exists for the conventional automated frequency allocation technologies.
In general, a number of measurement-based automatic frequency planning solutions exist in the prior art. These solutions are typically based on an approach that obtains local measurement information to make decentralized reallocation decisions. In other words, these solutions may leave the radio environment improved for one cell, but can still be deteriorated for another cell.
Also, another shortcoming of the existing automated frequency planning approaches is that the signal quality in different parts of a cellular network can fluctuate, sometimes very widely. Consequently, a decision for two cells relatively close to each other may be to change them to the same channel, which can result in high (possibly higher than before) interference levels, even after the frequency reallocations have occurred. However, as described in detail below, the present invention successfully resolves these problems.
In accordance with a preferred embodiment of the present invention, a method and system are provided for making multiple frequency reallocation decisions, which can be based on a single set of radio channel measurements. A consideration area (CA) is defined for each cell in a set of cells being optimized for a frequency plan. For example, a CA for a cell can be defined in terms of a distance between cells, radio attenuation between cells, and/or a handover order for neighboring cells (e.g., all 2nd order or neighbors"" neighboring cells). For the preferred embodiment, a frequency or channel reallocation made in a cell may not be detected outside of that particular cell""s CA. As such, the frequency plan can be optimized by determining all reallocations whereby local allocation-beneficial suggestions are found. For example, if a cell""s CA is defined as its 1st order neighbors, these beneficial suggestions can be consistency determinations (e.g., set of rules) that apply to that cell and its contiguous (1st order) neighbors.
An important technical advantage of the present invention is that new frequency or channel reallocations do not require that additional radio channel measurements be made.
Another important technical advantage of the present invention is that it is possible for an automatic frequency allocation algorithm to make numerous frequency or channel reallocations while still monitoring the quality improvement and/or impairment of neighboring cells.
Still another important technical advantage of the present invention is that a CA for cells can be defined, which can be used to increase the number of frequency or channel reallocations made per radio channel measurement period.
Yet another important technical advantage of the present invention is that a CA for cells can be defined, which can be used to decrease the number of frequency or channel reallocations made per radio channel measurement period, in order to increase the reliability of the resulting reallocations.